High-temperature soldering has been carried out for soldering various electronic parts in assembling processes such as a die-bonding of power transistor devices. For the high-temperature soldering, solder alloys having relatively high melting point of around 300 to 400° C. (hereinafter, also referred to as “high-temperature solder alloys”) have been used. For the high-temperature solder alloys, a Pb-based solder alloy as represented by Pb-5 mass % Sn has been conventionally used.
Notwithstanding the above, restrictions on the use of Pb have become increasingly stringent these days due to concern about environmental pollution. For example, RoHS Directive has already designated Pb as a restricted substance. In response to this trend, there is a demand for providing a solder alloy containing no lead, i.e., a Pb-free solder alloy, in a technical field of assembling electronic parts and the like.
As for solder alloys for low- and medium-temperature service (about 140 to 230° C.), Pb-free solder alloys mainly containing Sn have already been practically used. For example, Patent Document 1 discloses a Pb-free solder alloy composition containing Sn as a major component, 1.0 to 4.0 mass % of Ag, 2.0 mass % or less of Cu, 0.5 mass % or less of Ni, and 0.2 mass % or less of P. Further, Patent Document 2 discloses a Pb-free solder alloy composition containing 0.5 to 3.5 mass % of Ag, 0.5 to 2.0 mass % of Cu, and the balance Sn.
On the other hand, as for the high-temperature solder alloys, in order to provide a Pb-free solder alloy, a Bi-based solder alloy and a Zn-based solder alloy have been developed by various organizations. For example, as for the Bi-based solder alloy, Patent Document 3 discloses a Bi/Ag brazing filler material containing 30 to 80 mass % of Bi and having a melting temperature of 350 to 500° C. Further, Patent Document 4 discloses a production method of an alloy by adding a binary eutectic alloy to an eutectic alloy containing Bi and by further adding an additive element thereto, which makes it possible to adjust liquidus-line temperature and to reduce variations in composition.
As for the Zn-based solder alloy, Patent Document 5 for example discloses a high-temperature Zn-based solder alloy which is formed by adding Ge or Mg to a base material of a Zn—Al alloy, in which Al is added to Zn in order to decrease its melting point. Patent Document 5 also discloses a technique of further adding Sn or In, which has an effect to further decrease the melting point.
Specifically, Patent Document 5 discloses the following Zn alloys: a Zn alloy composition containing 1 to 9 mass % of Al, 0.05 to 1 mass % of Ge, and the balance being Zn and inevitable impurities; a Zn alloy composition containing 5 to 9 mass % of Al, 0.01 to 0.5 mass % of Mg, and the balance being Zn and inevitable impurities; a Zn alloy composition containing 1 to 9 mass % of Al, 0.05 to 1 mass % of Ge, 0.01 to 0.5 mass % of Mg, and the balance being Zn and inevitable impurities; a Zn alloy composition containing 1 to 9 mass % of Al, 0.05 to 1 mass % of Ge, 0.1 to 25 mass % of Sn and/or In, and the balance being Zn and inevitable impurities; a Zn alloy composition containing 1 to 9 mass % of Al, 0.01 to 0.5 mass % of Mg, 0.1 to 25 mass % of Sn and/or In, and the balance being Zn and inevitable impurities; a Zn alloy composition containing 1 to 9 mass % of Al, 0.05 to 1 mass % of Ge, 0.01 to 0.5 mass % of Mg, 0.1 to 25 mass % of Sn and/or In, and the balance being Zn and inevitable impurities.